The urinary bladder has two major functions; storage and voiding of urine. Contraction and relaxation of the urinary bladder smooth muscle (UBSM) is crucial to these tasks. Sympathetic nerves maintain relaxation of the bladder during filling via stimulation of (3-adrenoceptors. However, the exact physiological mechanisms by which P-adrenergic stimulation relaxes UBSM is unknown. Urinary incontinence is a common urogenital disease that can lead to life-threatening kidney problems. The most widespread type of incontinence, urge incontinence, is a result of increased UBSM contractions. Evidence suggests that defects in UBSM receptors or ion channels, such as the large conductance Ca2+-activated K+ (BK) channel and the small conductance Ca2+-activated K+ (SK) channel may underlie certain forms of urinary bladder dysfunction, including urge incontinence. We recently demonstrated that BK channel can be activated upon P-adrenergic stimulation to promote UBSM relaxation via a Ca2+-dependent mechanism (Petkov & Nelson, 2005, American Journal of Physiology). This project will focus on elucidating the cellular and molecular mechanisms by which P-adrenergic stimulation promotes UBSM relaxation. The overall hypothesis is that P-adrenergic stimulation relaxes UBSM via mechanisms, involving BK and SK channels, sarcoplasmic reticulum (SR) Ca2+ and urothelium. Specific aim 1 will elucidate the mechanisms by which P-adrenergic stimulation activates BK channels; Specific aim 2 will elucidate the role of sarcoplasmic reticulum (SR) Ca2+ in P-adrenergic UBSM relaxation; Specific aim 3 will elucidate the roles of SK channels and the urothelium in P-adrenergic relaxation of UBSM. We will use an integrated approach, combining electrophysiological, Ca2+ imaging, molecular biology, as well as in vivo and in vitro functional studies on bladder contractility in normal and genetically engineered mice to address the fundamental issue of P-adrenergic regulation of UBSM function. Establishing the exact molecular mechanisms of UBSM P-adrenergic relaxation will provide new potential therapeutic targets for treating urinary incontinence.